Legal Insurrection notes the 100th anniversary of the United States entering World War I.
Right before America joined, the Allies began to fall apart. Russia faced a revolution in February 1917 that forced Tsar Nicholas II to abdicate and saw the rise of the Communists. British and French forces could not fill in the holes left by the fallen soldiers. The Allies needed the Americans. The U.S. government established the Selective Service Act in 1917, which brought in 2.8 million men and 10,000 arrived in Europe every day. So while the Allies replaced their losses, the Germans could not: